Minimal coverings in the Rogers semilattices of -computable numberings.
On a hierarchy of groups of computable automorphisms.
On a sufficient condition for strong constructivizability of atomic Boolean algebras.
On classifying subsets of natural numbers by their computable permutations.
On computable formal concepts in computable formal contexts.
On constructive nilpotent groups.
On constructivizability of the tensor product of modules.
On problems of databases over a fixed infinite universe
In the relational model of databases a database state is thought of as a finite collection of relations between elements. For many applications it is convenient to pre-fix an infinite domain where the finite relations are going to be defined. Often, we also fix a set of domain functions and/or relations. These functions/relations are infinite by their nature. Some special problems arise if we use such an approach. In the paper we discuss some of the problems. We show that there exists a recursive...
On representability of P. Martin-Löf tests
On the Ershov upper semilattice .
On the hierarchies of Δ20-real numbers
A real number x is called Δ20 if its binary expansion corresponds to a Δ20-set of natural numbers. Such reals are just the limits of computable sequences of rational numbers and hence also called computably approximable. Depending on how fast the sequences converge, Δ20-reals have different levels of effectiveness. This leads to various hierarchies of Δ20 reals. In this survey paper we summarize several recent developments related to such kind of hierarchies shown by the author and his collaborators. ...
On the problem of finite signature.
On the reducibility of the index sets of families of general recursive functions.
On the relation of -reducibility between admissible sets.
Recursion theoretic operators and morphisms on numbered sets
Representability of recursive P. Martin-Löf tests
Restrictions on the degree spectra of algebraic structures.
Results on automorphisms of recursively saturated models of PA
Reverse mathematics of some topics from algorithmic graph theory
This paper analyzes the proof-theoretic strength of an infinite version of several theorems from algorithmic graph theory. In particular, theorems on reachability matrices, shortest path matrices, topological sorting, and minimal spanning trees are considered.
Some remarks on completions of numberings.